1. Field of the Invention
The present invention relates to a lead frame, e.g., a lead frame for a semiconductor device, and a semiconductor device using the lead frame. More particularly, the lead frame is connected to a semiconductor chip and is led out of the chip for connection to an external device.
2. Description of the Related Art
A lead frame for use in a resin-molded semiconductor device is required to meet that wires connecting a semiconductor chip and inner leads have a good wire bonding property, and joint portions of outer leads to an external device have good a soldering property.
For that reason, it has been hitherto customary to form a film of Pd (palladium) or a Pd alloy on an entire surface of a lead frame directly or through an undercoat, and then a thin film by Au (gold)-plating on the film of Pd or a Pd alloy.
Such an Au-plated film serves as a protective film for the film of Pd or a Pd alloy, and prevents the film of Pd or a Pd alloy from deteriorating due to oxidation. Also, even though formed thin, the Au-plated film is not adversely affected by the underlying film of Pd or a Pd alloy, and therefore can maintain a good soldering property specific to Au itself. Thus, characteristics of Pd and Au are exhibited to maximum, and a very good soldering property is achieved.
However, the above related art of forming the Au-plated film and the film of Pd or a Pd alloy on the entire lead frame is extremely uneconomical because expensive materials are used in excessive amount to cover even an area of a resin-molded semiconductor device where those films are not necessarily required.
Also, adhesion of the Au-plated film to a molding resin used in the resin-molded semiconductor device is so poor that a die pad and the resin tend to separate because of the presence of the Au-plated film. Therefore, cracks are more likely to occur in the resin covering corners of the die pad.